1. Field of the Invention
The present invention relates to a power shut-off method for an injection molding machine suitable for use in shutting off electrical power supply (hereinafter simply referred to as “power”) by use of a power switch.
2. Description of the Relevant Art
Generally, a molding process of an injection molding machine involves a lockup state of a mold clamping unit having a toggle link mechanism (in mold clamping step), and a nozzle touch state of an injection unit (in an injection step), etc., in which high pressure is applied to relevant components.
When power is shut off while high pressure is applied to relevant components, the state in which high pressure is applied to relevant components continues even after power shut off, because a drive section for applying the high pressure stops while maintaining the high pressure. This causes a failure or deterioration in an early stage (short life). Therefore, in an injection molding machine, some measure must be taken in order to cope with unexpected power shut-off in the middle of a step in which high pressure is applied to relevant components.
A conventional measure for coping with a power failure, which is unexpected power shut-off, is a mold-clamping selection method for a toggle-type mold clamping apparatus disclosed in Japanese Patent Application Laid-Open (kokai) No. 8(1996)-244083. Under this mold-clamping selection method, an offset amount of a toggle link mechanism of the toggle-type mold clamping apparatus is set by use of a setting device, and when power is shut off in the middle of a mold clamping step, the toggle link mechanism is selectively brought into a locked state or an unlocked state.
However, the above-described conventional power shut-off method (mold-clamping selection method) is based on the premise that when power is shut off, the interruption of a molding process stemming from power shut-off cannot be avoided. Incidentally, unexpected power shut-off occurs not only in the case of power failure but also in the event of other accidents; e.g., in the case where an operator mistakenly turns the power switch off when mistaking a different switch for the power switch, and the case where an article hits the power switch and turns the power switch off. In such a case, the conventional power shut-off method (mold-clamping selection method) shuts off the power immediately, whereby a molding process is interrupted, resulting in a drop in productivity and a delay in production schedule. Moreover, when an unlock state is selected, an unexpected operation may take place, possibly impairing the safety of the operator.